The proposal deals with the mechanism of transduction in both taste and olfaction. In the case of taste, two methods are proposed. The first is an in vivo method using the rat which allows the monitoring of the integrated chorda tympani response and the transepithelial potential or short-circuit current. Pulsed current or voltage also allows for a continuous record of the conductance. The second method utilizes the isolated lingual epithelium in vitro. This method allows the investigation of the effect of various pharmacological agents on the ion transport properties of the lingual epithelium. There is now evidence that one type of sodium taste receptor is a sodium transport pathway in the apical membranes of taste-bud cells. There is also good evidence that the apical transport pathway is also found in nongustatory epithelia. Thus, the short-circuit current averaged over a section of lingual epithelium is probably a good indicator of the current density across taste-bud cells. By recording the time course of the transepithelial potential or short-circuit current and the neural response, the tissue electrophysiological responses can be correlated with those seen in the gustatory nerves. Preliminary data indicate that the onset of neural activity coincides with the inward movement of current and that neural adaptation coincides with the slow or second component in the short-circuit current. Pharmacological probes, such as, amiloride, will be used to see if neural inhibition coincides with inhibition of the short-circuit current. The in vitro method will permit the study of zwitterions which inhibit the salt-evoked inward current and cetylpyridinium chloride, a recently discovered enhancer of the lingual transepithelial current. The development of an in vitro preparation of bullfrog olfactory mucosa promises to yield information on both olfactory secretory mechanisms and on the ionic basis of the odorant-stimulated inward current. When the ciliated side is stimulated with odorants, the response is a rapid inward current transient followed by a slower second inward current. The first component is probably of receptor cell origin. The results should establish the identity of the current carriers during the early phases of olfactory transduction.